1. Field of the Invention
This invention relates generally to Electronic Transmission Systems and, more specifically, to a Method and System for Emitter Identification Using Transmission Signatures.
2. Description of Related Art
Wireless communications involves the use of emitters (transmitters, transceivers, etc.) to transmit their signals electromagnetically. From a signal intelligence point of view, there are obvious advantages in being able to uniquely identify one emitter from the next. In the past, the methods that were employed to do this would identify each emitter by observing certain output signal characteristics. Prior art methods utilized time-domain based observations, or “RF fingerprints”, to differentiate one emitter from the next. These methods are not extremely accurate and have certain limitations.
What is needed therefore in the communications industry is an improved method and technique that identifies emitters more accurately than is normally done today. The invention described herein provides such an improved method, through the utilization of frequency-domain based observations, as opposed to the previous time-domain based methods. The ability to detect, store, compare, and analyze these frequency-domain based observations, or “transmission signatures”, for the purposes of emitter identification is the subject of this disclosure.
Each electronic emitter has electronic components called oscillators which are used to generate the various emitter's output frequencies. These oscillators inherently have very unique emission profiles in terms of subcarriers (intentional and non-intentional) and ramp up times, among others. The differences between emitters' oscillators arise due to fabrication, tuning, unit assembly, temperature, physical layout, manufacturing tolerances, and supporting component tolerances.
At the start of each transmission, an emitter's oscillators must output very specific frequencies in order to achieve the desired output frequency. As the oscillators are energized, they typically take several milliseconds to lock into their correct frequencies. In addition, their unique harmonics will interact with each other over this “key up” time period. This frequency-based profile over time of the way in which the oscillators key up to their final frequencies is what is referred to herein as the transmitter's “transmission signature”. It is this transmission signature that is detected and analyzed (uniquely) by this invention so that each emitter can be identified when its signals are received.
In conclusion, insofar as the inventor is aware, no invention formerly developed provides this unique method to identify emitters by their transmission signatures.